1. Field of the Invention
The present invention relates to a recording member for the electrographic recording of toner images thereon and to a coating for the recording member, which coating provides the member with electrical, optical, and durability characteristics useful for the recording process.
2. Description of the Prior Art
Kotz, U.S. Pat. No. 3,816,840 discloses an electrographic recording process and apparatus in which a dielectric recording member is arranged between two electrodes. Magnetically adhered to one of the electrodes is electronically conductive toner powder. The toner powder provides an electrically conductive path between the electrode to which it is bound and the adjacent surface of the dielectric member. A voltage is applied to the electrodes for a time and of a magnitude sufficient to generate a force pattern on the toner which enables toner deposition on the recording member in accordance with the force pattern. The force pattern is generated directly on the toner rather than on the recording member, which is passive in the operation of the apparatus disclosed in the patent.
For certain purposes in the practice of the recording process disclosed in U.S. Pat. No. 3,816,840, it is desirable that charge leakage from the recording member be such that a controlled amount of charge is dissipated from the toner deposited thereon, for example, from electrically charged toner applied uniformly to the recording member from an applicator member such as described in U.S. Pat. No. 4,402,000. One benefit of such controlled charge leakage is that the recording member can be re-imaged with no observation of a residue of a previous image pattern that will interfere with the new image on the recording member.
Resistance to mechanical damage, abrasion, and wear are important characteristics for the receptor surface of a recording member employed in a process where an appreciable number of images are required to be applied thereto and removed therefrom. These characteristics of durability can be judged by subjecting a receptor surface to repeated cycles of the process and observing the images produced for signs of catastrophic failure or gradual deterioration. The number of cycles completed while retaining the ability to produce images meeting the acceptance criteria is a measure of the surface's durability.
It is often desirable to apply the toner to a dielectric recording member which has a background color which offers high contrast to the toner powder. For example, if the contrast between toner powder and the recording member to which it is applied were sufficiently high, e.g. 0.6 optical density units, the recorded information could be read directly or indirectly, or even copied by optical means, all with high fidelity and high resolution. Then, the untransferred, unfixed toner powder could be removed from the recording member and new information could be displayed thereon. A system employing a recyclable toner powder could then be designed to optimize the quality of the displayed image without regard to its transfer and fixing properties, or to the cost of depleting the toner powder with each copy.
Anodized aluminum is the current recording member of preference. An aluminum oxide surface that has the appropriate electrical response can be formed on an aluminum substrate by anodization or other conventional means. However, it is well known that such surfaces change over time, particularly when subjected to environments having high relative humidity. This change may adversely affect the electrical characteristics of the aluminum oxide surface. Furthermore, in environments of high relative humidity, aluminum oxide surfaces tend to collect a film of moisture that must be removed by special means to assure a stable electrographic process. Finally, anodized aluminum and other such surfaces do not have the optical properties desirable for certain desirable applications of the process disclosed in the Kotz patent.
A receptor surface for a dielectric recording member, which surface will exhibit sufficient conductivity for the electrographic process, can be prepared by incorporating ionic materials in a dielectric organic resin, such as polyester resin; however, if the desired conductivity is dependent upon the presence of sufficient moisture to cause ionic movement and charge transfer, such a receptor surface will not perform satisfactorily in an environment of low relative humidity.
Other materials for a receptor surface which have appropriate electrical characteristics for use in a rapid cycle electrographic recording process generally are unable to withstand the mechanical abuse resulting from flexing, cycling, and the application and removal of toner powder.
A polyester film bearing an appropriate pigment can provide the desired contrast between recording member and toner powder. However, a polyester film, or a film prepared from another dielectric organic resin, when applied to a conductive grounding surface, will generally not allow charge to flow through it or leak from its surface fast enough to allow removal of one image from the surface of the film and replacement with another image during a commercially acceptable cycle of the electrographic recording device.
Thus, it can be seen that selection of a recording member and dielectric coating thereof for use with a recyclable imaging powder may be constrained by at least three factors:
(1) Electrical properties of the recording member must allow balance between dielectric properties and sufficient charge leakage from the toner so that the toner can be imagewise deposited and thereafter removed from the recording member surface within certain predetermined times (or equivalent distances), such as between an applicator member and the styli array, and/or removal of and replacement of toner powder within one operating cycle of the process;
(2) Durability properties of the recording member must be sufficient in order to allow the process to be economically feasible;
(3) Contrast between the toner powder and the recording member can be specified to be high, e.g. at least 0.6 optical density units.
Although it is relatively simple to provide a recording member that fulfills any one of the three foregoing constraints, satisfaction of all three of them simultaneously has heretofore proved to be extremely difficult.